Abstract
The mechanisms of cell movement on a solid surface are well illustrated by experiments carried out by A. Verkhovsky's group. Verkhovsky's group on keratocyte cells and their lamellipodia and fragments extracted from keratocytes.
A very simple lamellipod model in which the cytoskeleton is treated as an active gel can be made in two dimensions (the direction of movement and the direction perpendicular to the substrate). It assumes that polymerization occurs at the front of the lamellipod and depolymerization at the rear. This model shows that the speed of advance is linked to the speed of depolymerization (or polymerization). It also predicts a retrograde actin flow in the opposite direction to the movement, due to the contractility of the cytoskeleton, whose speed is lower than the speed of the cell. The lamellipod thickness profile corresponds well to that observed experimentally.
Spontaneous movement of keratocyte fragments enables us to study cytoskeletal polarization. By neglecting cell thickness and studying the stability of a circular fragment, we show that fragment instability is due to polymerization and depolymerization processes, and that the instability resembles a classical Saffman-Taylor instability.
